public class DecimalsSum {
    public static void main(String[] args) {

            double sum=0;//分子式之和要用浮点数存储

        for (int i = 1; i <=100; i++) {
            if(i%2!=0){
                sum=sum+1.0/i;
            }
            else sum=sum-1.0/i;

        }
        System.out.println(sum);
    }
}